1. Field of the Invention
The present invention relates to a laser gyro, a semiconductor laser gyro, a method for driving the laser gyro and the method for driving the semiconductor laser gyro and, in particular, to a laser gyro of ring resonator type.
2. Related Background Art
Heretofore in the past, there have been known mechanical gyros having rotors and transducers or optical gyros as gyros for detecting the angular speed of a moving object. Since the optical gyros in particular are capable of starting up instantaneously and have a wide dynamic range, they are bringing about a revolution in the field of gyro technology.
The optical gyros include laser gyros, optical fiber gyros, passive resonator gyros and the like. Among them, a laser gyro employing a gas laser was most early undertaken to develop and already put to practical use in the art of aircrafts and the like.
Recently, as a small and highly accurate laser gyro, a semiconductor laser gyro integrated on a semiconductor substrate is proposed, which is disclosed, for example, in Japanese Patent Application Laid-Open No. 5-288556. This specification discloses a technique for taking out laser beams propagating in a clockwise direction and a counterclockwise direction respectively from laser elements of ring ridge type and for causing them to interfere with each other and taking out an interference intensity as photocurrent.
Also, in Japanese Patent Application Laid-Open No. 57-43486 (U.S. Pat. No. 4,431,308), a gyro is disclosed, which utilizes a change in the terminal voltage of the above described element with rotation without taking out light from the semiconductor laser element.
In FIG. 29, a semiconductor laser element 5792 has electrodes 5790, 5791 above and below it. Reference numeral 5793 denotes a direct current blocking capacitor, reference numeral 5794 an output terminal, and reference numeral 5795 a resistor. It is disclosed that, as shown in FIG. 29, the semiconductor laser element as a laser element for the ring laser device is connected to a driving power source 5796, and a frequency difference (a beat frequency) between light beams clockwise and counterclockwise generated when a certain angular speed is given to the above device is detected as a difference between the terminal voltages of the laser element.
Also, it is further disclosed in Japanese Patent Application Laid-Open No. 4-174317 that a change in the terminal voltage of the laser element which is generated with rotation is detected.
However, the conventional laser gyro cannot detect a rotation direction. This is because the beat frequencies detected from the terminal voltage has the same value whether the rotating direction of the semiconductor laser element is clockwise or counterclockwise. For this reason, dithering was effected and, from the correlation between the direction and signal of the dither, the rotating direction was determined.
Also, in the laser gyro, with a rotation, oscillating frequencies are divided into two. However, when the rotation speed is small, a difference between the oscillating frequencies becomes small. In this case, because of non-linearity in the medium, a rock-in phenomenon occurred, wherein the oscillating frequencies were drawn into another mode. In order to release this rock-in phenomenon, the dithering of the laser gyro is conducted.
It is an object of the present invention to provide a laser gyro, a semiconductor laser gyro, a method for driving the laser gyro and a method for driving the semiconductor laser gyro, in which the direction of a rotation can be detected even when a mechanical device such as a dither is not disposed, and hard to cause a rock-in phenomenon.
The ring laser gyro according to the present invention is a ring laser gyro in which first and second laser beams propagate in opposite directions from each other, characterized in that plural electrode areas are provided on an optical waveguide comprised in the ring laser, and current injected or voltage applied to the electrode areas is controlled, so that the oscillating frequencies of the first and second laser beams become different from each other at a time when the ring laser gyro is in a stationary state.
The above control is such that current is injected to the plural electrodes so that a space in which the refractive index of the optical waveguide is modulated moves in the same direction as the propagating direction of the first or second laser beam as time goes on.
Also, the above control is such that injected current is propagated in the same direction as the propagating direction of the first or second laser beam.
A method for driving the ring laser gyro according to the present invention is characterized in that a space in which the refractive index of an optical waveguide is modulated moves in one propagating direction as time goes on.
Also, the method for driving the ring laser gyro according to the present invention is a method for driving ring laser gyro having plural electrodes, characterized in that voltage applied or current injected to the plural electrodes is modulated with a time difference set among the electrodes so that a sequence of modulations is in a propagating direction.
Also, the method for driving the ring laser gyro according to the present invention is a method for driving the semiconductor laser gyro in which by flowing the current to generate laser oscillation light is propagated in one propagating direction or in the propagating direction opposite to the one propagating direction, characterized in that the flowing direction of the current is limited to the one propagating direction.